Thiosulfate Gold Leaching by Chromafora – High Yield and Low Costs Confirmed in Pilot

Chromafora’s pilot project for a non-cyanide gold extraction process has recently been formally reported to and fully approved by Sweden’s innovation agency and co-funder Vinnova. The results demonstrate a groundbreaking method with high yield—so far up to 92 percent—combined with a competitive economic outlook.

The Swedish impact company Chromafora has successfully developed a pioneering gold extraction process. The method is cost-efficient and entirely non-toxic and has the potential to become the first profitable alternative to conventional and hazardous cyanide leaching.

“Our method eliminates the toxic risks associated with cyanide and makes it possible to refine the ore and gold concentrates directly at the mine site instead of transporting them elsewhere. This benefits local communities and reduces transportation needs,” explains Johan Berg, Application Manager at Chromafora and project lead for the gold leaching initiative.

High gold prices have increased interest in gold recovery from both primary mining operations and secondary streams such as end-of-life electronics. Many countries have already banned cyanide leaching, creating a strong demand for a competitive and environmentally friendly alternative.

The objective of the pilot project was to further develop the combination of a thiosulfate-based lixiviant and Chromafora’s metal separation technology, Selmext, and to demonstrate its economic and environmental potential. The test was conducted in collaboration with a mining company between 1 March 2022 and 30 March 2025. Pilot-scale leaching yields ranged from 53–92 percent, while laboratory yields were between 80–86 percent. In addition, recovery of the Selmext and catalytic reagents showed that up to 96 percent recycling is possible. This result contributes to economic competitiveness.

“When we assess a hypothetical full-scale plant with a capacity requirement of processing 15,000 tonnes of gold concentrate per year, the total operating cost of Chromafora’s gold leaching process is comparable to that of conventional cyanide leaching,” says Johan Berg.

The gold leaching work is now entering a new phase. A demonstration plant is currently being commissioned, and the door is open to new collaborations, with the goal of becoming the a commercial alternative to cyanide leaching.

Advantages of Chromafora’s Gold Leaching Method

• Non-toxic and based on a limited number of well-known chemicals
• A cost-efficient thiosulfate-based method
• Enables internal, direct recycling of almost all process chemicals
• Suitable for on-site leaching and gold recovery at the mine, benefiting local communities and reducing transportation

About Chromafora’s Gold Leaching Method
Chromafora’s gold leaching method is a cyanide-free hydrometallurgical gold extraction process in which a thiosulfate-based lixiviant is combined with Chromafora’s metal separation technology, Selmext. Selmext addresses a key limitation of the well-known but deficient thiosulfate leaching method by efficiently separating metal impurities from the gold-enriched lixiviant solution and thereby enabling effective final gold extraction.

The project was divided into research and pilot phases. Pre-treatment and leaching were primarily carried out by Luleå University of Technology, Sweden, while the pilot was conducted by Chromafora in collaboration with the Björkdalsgruvan mine, a gold mine in northern Sweden.